Many display devices exist within the market today. Among the displays that are available are thin-film, coated, Electro-Luminescent (EL) displays, such as OLED displays. These displays can be driven using active matrix backplanes, which employ an array of active circuits. These active circuits control the flow of current to each light-emitting element in the display. However, these displays tend to be relatively expensive due to the complexity of forming an active circuit at each light-emitting element and the thin film transistors that are often used within these active drive circuits are prone to defects, leading to lack of uniformity or threshold shifts over time, which degrade the quality of the display.
Passive matrix thin-film, coated, electro-luminescent displays are also known. Unfortunately, these displays typically allow only one line of the display to be driven simultaneously, typically using pulse width modulation. Further, it is typically necessary in these devices to discharge and charge the capacitance of each light-emitting element before each lighting cycle. For these reasons, passive matrix, thin-film, coated electro-luminescent displays typically draw excessive amounts of power and often require drive voltages that are larger than can be provided by row and column drivers that are manufactured using low-cost silicon manufacturing processes whenever the displays exceed some dimension, which today is less than 2 inches in diagonal.
Recently, multiline passive matrix drive methods that are applicable to EL displays have also been discussed in the literature. Among these approaches, are a method described by Yamazaki et al. in U.S. patent application Ser. No. 10/680,221, entitled “Image Display Apparatus” and a separate method described by Smith et al. in PCT filings WO 2006/035246 entitled “Multi-Line Addressing Methods and Apparatus”, WO 2006/035248 entitled “Multi-Line Addressing Methods and Apparatus” and WO 2006/067520 entitled “Digital Signal Processing Methods and Apparatus”. Each of these methods can be used to significantly reduce the current through each light-emitting element within an EL display and to potentially reduce the peak current on individual row lines. This then reduces power losses due to the resistance of the row and column electrodes within these displays and, under certain drive conditions, can also reduce the power dissipated to charge and discharge the capacitance of the display, making it possible to build larger passive matrix EL displays with reasonable power dissipation. Unfortunately, these methods often introduce some errors into the data signal, which can result in image artifacts under certain conditions. Further, they only allow the size of passive matrix EL displays to be increased by a factor of a few, rather than a factor of 10 or more as would be desired.
Another method for forming larger passive matrix displays is to form several individual displays or displays with multiple row and column drivers, which serve as tiles that are bonded together to form a larger EL display. Such tiled displays are well known in the art. For example, Nimmer et al. in U.S. Pat. No. 6,980,182, entitled “Display System” and Cok et al. in U.S. Pub. No. 2006/0108918, entitled “Tiled OLED Display” each discuss forming a single display substrate to which multiple row and column drivers can be attached to provide a tiled display with a larger area than can be achieved using a single display employing a single row and column driver. Such a method allows multiple EL tiles to be formed by coating uniform light-emitting layers, eliminating a significant source of non-uniformity between tiles. Such an arrangement is beneficial in passive-matrix EL displays since each row driver provides a signal to only a subset of the row electrodes within the final tiled display. Since the number of times that the capacitance of such a display must be charged and discharged is proportional to the number of lines that are driven and the power dissipated by such a display when using a one line at a time passive matrix drive method increases by approximately the square of the number of lines that are driven, such a method allows the drivers to drive half the total lines in the display and can, therefore, significantly reduce the power consumption of the display, again allowing the size of a display having reasonable power consumption to be increased by a factor of 2 or 3. These disclosures do not discuss the combination of multi-line drive methods together with the tiling of passive matrix EL displays. Freidhoff and Phelan have discussed other tiled EL displays in U.S. Pat. No. 6,509,941, entitled “Light-Producing Display Having High Aperture Ratio Pixels” and U.S. Pat. No. 6,853,411, entitled “Light-Producing High Aperture Ratio Displays Having Aligned Tiles”.
One issue with tiled displays, is that an input image signal 122 is typically streamed into such a display in a raster fashion, starting with the data point at the top left corner of the image and then sequentially providing data for pixels in each row of the display. However, since the displays have separate row and column drivers for each tile, it is typically necessary for a higher level controller to store this input image signal as it is received, segment the input data into independent blocks and then provide each independent block of input image signal data to the row and column driver wherein each block of input image signal data will be used by the row and column drivers connected to each tile to independently render the portion of the input image signal that corresponds to the physical location of the tile within the display. For example, in U.S. patent application Ser. No. 10/158,321, by Koester et al. and U.S. patent application Ser. No. 10/249,954 by Lin, each discuss using a processor to store and reorganize the input image signal into multiple, independent blocks wherein each block is independently distributed to the row and column drivers for each tile.
One of the dominant problems in such displays arises because the human visual system is extremely sensitive to changes in luminance or artificial luminance edges that occur near the boundary between adjacent tiles. It is known to sort tiles to reduce luminance differences as discussed by Greene et al., in U.S. Pat. No. 5,668,569, entitled “Tiled, Flat-Panel Displays with Luminance-Correcting Capability” and U.S. Pat. No. 6,292,157, entitled “Flat-panel Display Assembled from Pre-sorted Tiles Having Matching Color Characteristics and Color Correction Capability”. Further, it is known to adjust the input image signal to reduce differences in color or luminance of images at the boundary between edges of adjacent tiles as discussed by Green et al. in U.S. Pat. No. 6,271,825, entitled “Correction Methods for Brightness in Electronic Display”. In the color and luminance correction methods discussed in these patents, data describing the radiometric performance of each of the tiles that form the display are used to adjust the input image signal before this input image signal is provided each of the row and column drivers. It is worth noting that these approaches correct only for differences between the optical performances of neighboring tiles. The row and column drivers within the embodiments discussed within these disclosures operate independent of one another as each receives and responds to individual blocks of the input image signal.